1. Field of the Invention
This invention relates to a magnetic disk cartridge. This invention particularly relates to an improvement in a temporary assembly structure of a pair of cassette shell halves in a magnetic disk cartridge comprising a cassette shell, which is constituted of the cassette shell halves joined to each other, and a magnetic disk incorporated in the cassette shell such that it can rotate.
2. Description of the Prior Art
Magnetic disk cartridges comprise a thin type of cassette shell and a magnetic disk, which is incorporated in the cassette shell such that it can rotate and on which analog or digital signals are to be recorded magnetically. The cassette shell takes on the form of a flat prismatic shape and comprises a rectangular top surface having an area slightly larger than the area of the magnetic disk, a bottom surface having an opening, through which a center core for supporting the center of the magnetic disk is exposed to the exterior, and a side surface having a narrow width and extending between the periphery of the top surface and the periphery of the bottom surface. The magnetic disk cartridge is provided with an opening for insertion of a magnetic head, through which the magnetic head for magnetically recording and reproducing signals is to be inserted from the exterior such that the magnetic head can be brought into contact with the surfaces of the magnetic disk or can be brought to positions close to the surfaces of the magnetic disk. Also, the magnetic disk cartridge is provided with a shutter for opening and closing the opening for insertion of the magnetic head. When the magnetic disk cartridge is not used, the shutter closes the opening for insertion of the magnetic head such that dust, debris, or the like, may not enter into the magnetic disk cartridge. Liners constituted of nonwoven fabrics, or the like, are applied to the inner surfaces of the cassette shell, which stand facing the magnetic disk. When the magnetic disk is rotated, the liners serve to prevent the surfaces of the magnetic disk from being scratched and to remove dust, debris, or the like, from the surfaces of the magnetic disk.
In conventional magnetic disk cartridges, there is a sufficient spacing in the cassette shell along the thickness direction of the magnetic disk accommodated therein. Each of the liners is pushed up from the inner surface of the cassette shell by a weak leaf spring-like lifter. The liner is thereby urged toward the magnetic disk and kept in sufficient contact with the magnetic disk. Therefore, a slight allowance is tolerated for the dimensional accuracy in the thickness direction within the cassette shell.
Recently, a magnetic disk cartridge, which has a recording capacity 50 times as large as the recording capacity of the conventional magnetic disk cartridge (3.5-inch floppy disk) by virtue of a new high-density recording system, has been developed. In the developed magnetic disk cartridge, the magnetic disk is rotated at a markedly higher speed than the speed, at which the magnetic disk in the conventional magnetic disk cartridges is rotated. Also, when signals are recorded on the magnetic disk accommodated in the developed magnetic disk cartridge and are reproduced therefrom, the position of the magnetic disk must be adjusted with a very high accuracy with respect to a magnetic head.
A quality inspection is carried out in a final process of the operation for assembling a magnetic disk cartridge, and products having defects are removed as defective products. Defects encountered with magnetic disk cartridges include various kinds of defects. Since cassette shell halves are molded at a high accuracy and require a high manufacturing cost, in cases where a magnetic disk cartridge is regarded as a defective one due to defects of the magnetic disk incorporated therein, the cassette shell halves constituting the cassette shell of the magnetic disk cartridge should preferably be capable of being reused.
A magnetic disk cartridge comprises a cassette shell, which is constituted of a pair of cassette shell halves joined to each other, and a magnetic disk incorporated in the cassette shell such that it can rotate. Therefore, in the final process of the assembly operation, before the cassette shell halves, between which the magnetic disk has been interposed, are joined to each other by ultrasonic welding, or the like, a quality inspection should be carried out. In cases where defects are found for the magnetic disk, it should be exchanged with a new one. In this manner, the cassette shell halves can be reused.
Therefore, a structure of a magnetic disk cartridge is desired wherein, in the final process of the operation for assembling the magnetic disk cartridge, the cassette shell halves, between which the magnetic disk has been incorporated, can be temporarily fixed to each other, a quality inspection can be carried out before the cassette shell halves are joined to each other, and the cassette shell halves can be easily separated from each other in cases where a defect of the magnetic disk is found.
As the temporary assembly structures of audio and video cassettes, the structures for securing with screws have heretofore been employed. However, with thestructures for securing with screws, an internal thread for receiving an external thread becomes collapsed during repeated operations for securing with screws. Therefore, the internal thread can be reused only a limited number of times. Also, the operation for turning the screws with a screw driver must be carried out in order to engage and disengage the screws, and therefore the efficiency of the process cannot be kept high.
Therefore, a method for temporarily assembling cassette shell halves to each other has bee proposed, in which one of the cassette shell halves is provided with an engagement hole, and the other cassette shell half is provided with an engagement protrusion for fitting into and engaging with the engagement hole. However, with the proposed method, a slight clearance is set between the engagement hole and the engagement protrusion, and the cassette shell having been assembled temporarily undergoes a rattling motion. It has been found that it is difficult to rotate the magnetic disk quickly in such a rattling state, and quality inspection cannot be carried out satisfactorily.